1. Field of the Invention
This invention is directed to computing systems, in general, and to systems using a common memory which can be accessed by a plurality of microprocessors and includes systems wherein the microprocessor have different size words.
2. Prior Art
In the rapid expansion of computer system technology, it has become commonplace for devices called microprocessors to be used as portions of the computing systems. In many cases, the microprocessors are used as supplemental units or circuits to perform specific tasks or functions either under the direct control of the central processing unit (CPU) or as an adjunct thereto. In most cases, the microprocessor is arranged to have separate memory capability which does not interface with or interact with the main memory of the computing system. However, there are times when it is highly desirable to permit or even require an exchange of information between the processor and the computer system.
With the introduction of multiple microprocessors into many computer systems, it is almost essential that the microprocessors be able to communicate with each other. This situation has created problems inasmuch as many of the microprocessors have different word lengths, e.g. 16-bit or 8-bit words, which complicates the exchange of information. Moreover, the use of multiple microprocessors typically requires the use of multiple peripheral equipment such as memories an the like. This, of course, becomes expensive in terms of programming, hardware, system geography and the like. Consequently, it is highly desirable to have the microprocessors share as much as the peripheral equipment as possible. To this end, communication between the processors is highly desirable.
However, it must be understood that this communication requires appropriate data and/or command busses and addresses in the microprocessors. In addition, unless totally separate communication busses are provided, elaborate control of the bus may be required or inefficient utilization of the microprocessors will frequently occur. Consequently, it is highly desirable to provide computing systems wherein the microprocessors can communicate with each other irrespective of word length. It is further desirable to permit the microprocessors to exchange data and/or commands with a common memory without effectively locking one or more of the microprocessors off of a shared bus.